When former Mayor Bill de Blasio recently defended current Mayor Zohran Mamdani’s labeling of Israeli Prime Minister Benjamin Netanyahu as a “war criminal,” he pointed to one metric above all: the number of civilian casualties in Gaza. Mamdani and de Blasio are not alone. Throughout the progressive left and much of the press, the accusation of Israeli “war crimes” and “genocide” has quietly transformed into an accepted default narrative. But there’s a vital question almost nobody bothers to ask: If large civilian casualties alone prove war crimes or genocide, where does that logic stop? Harry Truman authorized the atomic bombings...